“Both Pelosi and Schumer know their foundational argument but will firm up their rebuttal in real time because of uncertainty surrounding where President Trump may lead the American people,” a source close to the preparations told The Post.

Speculation swirled prior to the 9 p.m. televised address over whether Trump would declare a national emergency, which could give him the power to order the construction of his long-promised border wall.

But even some conservative stalwarts warned that it should be a last resort, while Democrats vowed to fight any such decree in court.

“A national emergency declaration is an option but it should be the last option used,” said North Carolina Rep. Mark Meadows, co-founder of the hardline Freedom Caucus.

Multiple reports said Trump’s conservative friends and advisers are urging him to declare a national emergency to reopen the government and get funding for the wall.